1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to radio receivers utilized within such wireless communication systems.
2. Description of Related Art
As is known, wireless communication systems include a plurality of wireless communication devices and wireless infrastructure devices. The wireless communication devices, which may be radios, cellular telephones, stations coupled to personal computers, laptops, personal digital assistance, et cetera, communicate with each other via wireless communication channels that are administered by the wireless infrastructure devices. Such wireless infrastructure devices include base stations (e.g., for cellular wireless communication systems), access points (e.g., for wireless local area networks), system controllers, system administrators, et cetera.
As is also known, each wireless communication device and/or wireless infrastructure device includes a radio transceiver (i.e., a transmitter section and receiver section) to transmit and receive RF signals. A radio transmitter includes one or more intermediate frequency stages, a filter, a power amplifier, and coupling to an antenna. The one or more intermediate frequency stages mix an outbound baseband signal (e.g., data that has been encoded and/or modulated in accordance with a wireless communication standard such as IEEE802.11a, IEEE802.11b, Bluetooth, Global System for Mobile communications (GSM), Advance Mobil Phone System (AMPS), et cetera) with a local oscillation, or oscillations, to produce an outbound RF signal. The filter filters the outbound RF signal to attenuate unwanted frequency components of the RF signal and the power amplifier amplifies the filtered RF signal prior to transmission via the antenna.
The baseband processor of the transmitter produces outbound baseband signal at a given processing rate. Typically, the processing rate of the transmitting baseband processor is synchronized with the transmitting local oscillation or oscillations and is a fraction of the local oscillation, or oscillations.
As is also known, a radio receiver includes a low noise amplifier, one or more intermediate frequency stages, a filter, and a baseband processor. The low noise amplifier is coupled to receive an inbound RF signal via an antenna and amplifies the RF signal before providing it to the one or more intermediate frequency stages. The one or more intermediate frequency stages mix the amplified RF signal with a local oscillation, or oscillations, to produce an inbound baseband signal. The receiving baseband processor processes the baseband signal at a given processing rate to recapture data. Like the transmitter section, the processing rate of the baseband receiving processor is synchronized to, and is a fraction of, the receiver local oscillation or oscillations.
While wireless communication standards specify that the processing rate of both the transmitting and receiving baseband processors are to be the same and that the transmitter local oscillation or oscillations and the receiver local oscillation or local oscillations are to be the same, practical limitations of electronic circuitry makes it virtually impossible for the processing rates and local oscillations, from wireless communication device to wireless communication device, or wireless communication device to wireless infrastructure device, to be identical. As such, wireless communication standards, such as IEEE 802.11, specify an acceptable tolerance of variations of the processing rate and local oscillations from wireless communication device to wireless communication device and/or from wireless communication device to wireless infrastructure device. For example, the IEEE 802.11a specification specifies a tolerance of 20 PPM (parts per million) in each wireless communication device or wireless infrastructure device. As such, the local oscillation or oscillations, and processing rates from wireless communication device to wireless communication device and/or from wireless communication device to wireless infrastructure device, may be off by no more than a total of 40 PPM.
Due to the differences between the processing rates and local oscillations from wireless communication device to wireless communication device and/or wireless communication device to wireless infrastructure device, a receiver of a wireless communication device or wireless infrastructure device will almost certainly be operating at a different processing rate and having a different local oscillation or oscillations than the processing rate and local oscillations of the transmitter of another wireless communication device or wireless infrastructure device. This difference, when an RF signal is received, results in an offset within the receiver, which limits the receivers ability to accurately recapture data embedded within received RF signals.
Therefore, a need exists for a method and apparatus that increases a receiver's ability to accurately recapture data embedded within received RF signals.